Conventional variable pressure or environmental scanning electron microscopes, typically include a specimen chamber for receiving a specimen to be viewed. The specimen chamber is arranged in communication with an electron column at one end of which an electron source is arranged to provide a beam of electrons for interaction with the specimen in the specimen chamber. One or more detectors are provided to monitor a variety of signals resulting from interaction between the specimen and electrons in the beam. An example of such an ESEM is the FEI Philips ESEM.
The primary advantage of an ESEM over a conventional scanning electron microscope is that it permits a user to vary the sample environment i.e. the environment within the specimen chamber through a range of pressures, temperatures and gas compositions. In other words, the high vacuum constraints required in the specimen chamber of a conventional scanning electron microscope are not required in the specimen chamber of an ESEM. Due to this and other well known differences between an ESEM and a conventional scanning electron microscope specimens may be examined in an ESEM in their natural states e.g. wet, dirty, non-conductive etc.
There are a number of applications in which it is desirable to introduce liquid drops into the specimen chamber of an ESEM with a liquid firing device such as an inkjet print head so that the interaction between a liquid drop and a receiving surface can be viewed. For example, in the printing industry, research is conducted into the mechanism by which inkjet printing operates. In general, currently available systems and methods for introducing liquid into the specimen chamber of an ESEM are too coarse in that the size of the drops formed are too large and they are difficult to control. One example of such a system is the microinjector made by Oxford Instruments. This system can be difficult to control because it relies on the use of a complex system of tubes and valves. Furthermore, it does not provide any way of viewing the operation of an inkjet print head and the printing process from an inkjet print head under the magnification available from a scanning electron microscope.